U.S. patent number 10,280,689 [Application Number 15/437,629] was granted by the patent office on 2019-05-07 for polycrystalline superhard construction.
This patent grant is currently assigned to Element Six Abrasives S.A.. The grantee listed for this patent is Element Six Abrasives S.A.. Invention is credited to Nedret Can, Thembinkosi Shabalala.
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United States Patent |
10,280,689 |
Shabalala , et al. |
May 7, 2019 |
Polycrystalline superhard construction
Abstract
A polycrystalline superhard construction comprises a body of
polycrystalline superhard material, and a substrate of hard
material bonded thereto along an interface. The body of
polycrystalline superhard material comprises a first region
abutting the substrate along the interface and a second region
bonded to the first region. The second region defines a rake face,
a cutting edge, a chamfer and at least a part of a flank face, the
cutting edge being defined by an edge of the flank face joined to
the chamfer, the chamfer extending between the cutting edge and the
rake face. The height of the chamfer in a plane parallel to the
plane through which the longitudinal axis of the polycrystalline
superhard construction extends is less than the thickness of the
second region. The first region comprises a material having coarser
grains than the second region. There is also disclosed a method of
making the same.
Inventors: |
Shabalala; Thembinkosi
(Springs, ZA), Can; Nedret (Springs, ZA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Element Six Abrasives S.A. |
Luxembourg |
N/A |
LU |
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Assignee: |
Element Six Abrasives S.A.
(Luxembourg, LU)
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Family
ID: |
44511887 |
Appl.
No.: |
15/437,629 |
Filed: |
February 21, 2017 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20170183916 A1 |
Jun 29, 2017 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13534927 |
Jun 27, 2012 |
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61503420 |
Jun 30, 2011 |
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Foreign Application Priority Data
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Jun 30, 2011 [GB] |
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1111179.6 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B
10/567 (20130101); E21B 10/5735 (20130101); B01J
3/062 (20130101); E21B 10/36 (20130101); B01J
2203/062 (20130101); E21B 10/54 (20130101); E21B
10/55 (20130101); B01J 2203/0655 (20130101); B24D
18/0009 (20130101); B01J 2203/0685 (20130101) |
Current International
Class: |
E21B
10/573 (20060101); E21B 10/567 (20060101); E21B
10/36 (20060101); B24D 18/00 (20060101); B01J
3/06 (20060101); E21B 10/54 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2335682 |
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Sep 1999 |
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GB |
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2419364 |
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Apr 2006 |
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GB |
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2009128034 |
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Oct 2009 |
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WO |
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Primary Examiner: Bagnell; David J
Assistant Examiner: Hall; Kristyn A
Attorney, Agent or Firm: Bryan Cave Leighton Paisner LLP
Claims
The invention claimed is:
1. A polycrystalline superhard construction comprising: a body of
polycrystalline superhard material; a substrate of hard material
bonded to the body of polycrystalline superhard material along an
interface; wherein the body of polycrystalline superhard material
comprises a first region and a second region, the first region
abutting the substrate along the interface and the second region
being bonded to the first region along a further interface, the
second region defining a rake face, a cutting edge, a chamfer and
at least a part of a flank face, the cutting edge being defined by
an edge of the flank face joined to the chamfer, the chamfer
extending between the cutting edge and the rake face; the first
region having a first thickness and the second region having a
second thickness; the chamfer having a height in a plane parallel
to the plane through which the longitudinal axis of the
polycrystalline superhard construction extends, the height of the
chamfer being less than the thickness of the second region; the
first region comprising a material having coarser grains than the
material of the second region; wherein the thickness of the second
region is up to around 600 microns; and the thickness of the second
region exceeds the height of the chamfer by around between 100 to
400 microns.
2. A polycrystalline superhard construction according to claim 1
wherein the thickness of the first region is greater than the
thickness of the second region.
3. A polycrystalline superhard construction according to claim 1,
wherein the thickness of the first region is around 1200-1800
microns.
4. A polycrystalline superhard construction according to claim 1,
wherein the height of the chamfer is between around 100-400
microns.
5. A polycrystalline superhard construction according to claim 1,
wherein the body of polycrystalline superhard material comprises
polycrystalline diamond material.
6. A polycrystalline superhard construction according to claim 5,
wherein the average grain size of the diamond grains forming the
second region in the body of polycrystalline diamond material is
between around 0.1 to 10 microns.
7. A polycrystalline superhard construction according to claim 5,
wherein the average grain size of the diamond grains forming the
second region in the body of polycrystalline diamond material is
between around 1 to 8 microns.
8. A polycrystalline superhard construction according to claim 5,
wherein the average grain size of the diamond grains forming the
second region in the body of polycrystalline diamond material is
between around 3 to 6 microns.
9. A polycrystalline superhard construction according to claim 5,
wherein the average grain size of the diamond grains forming the
first region in the body of polycrystalline diamond material is
between around 6 to 20 micron.
10. A polycrystalline superhard construction according to claim 5,
wherein the average grain size of the diamond grains forming the
first region in the body of polycrystalline diamond material is
between around 8 to 17 microns.
11. A polycrystalline superhard construction according to claim 5,
wherein the average grain size of the diamond grains forming the
first region in the body of polycrystalline diamond material is
between around 6 to 17 microns.
12. A polycrystalline superhard construction according to claim 1,
wherein the chamfer angle is approximately 45.degree..
13. A polycrystalline superhard construction according to claim 1,
wherein the interface between the first region and the substrate is
substantially non-planar.
14. A polycrystalline superhard construction according to claim 1,
wherein the substrate comprises cemented carbide.
15. A cutter for boring into the earth comprising the
polycrystalline superhard construction according to claim 1.
16. A PCD element for a rotary shear bit for boring into the earth,
for a percussion drill bit or for a pick for mining or asphalt
degradation, comprising the polycrystalline superhard construction
of claim 1.
17. A drill bit or a component of a drill bit for boring into the
earth, comprising a polycrystalline superhard construction
according to claim 1.
Description
FIELD
This disclosure relates to a cutter comprising a superhard
construction, particularly but not exclusively for a rotary drill
bit for boring into the earth.
BACKGROUND
Polycrystalline diamond (PCD) material comprises a mass of
inter-grown diamond grains and interstices between the diamond
grains. PCD material may be made by subjecting an aggregated mass
of diamond grains to a high pressure and temperature in the
presence of a sintering aid such as cobalt, which may promote the
inter-growth of diamond grains. The sintering aid may also be
referred to as a catalyst material for diamond. PCD material may be
formed on a cobalt-cemented tungsten carbide substrate, which may
provide a source of cobalt catalyst material for sintering the PCD
material.
PCD material may be used in a wide variety of tools for cutting,
machining, drilling or degrading hard or abrasive materials such as
rock, metal, ceramics, composites and wood-containing materials.
For example, tool inserts comprising PCD material are widely used
in drill bits used for boring into the earth in the oil and gas
drilling industry. In many of these applications, the temperature
of the PCD material may become elevated as it engages rock or other
workpiece or body with high energy. The working life of tool
inserts may be limited by fracture of the superhard material,
including by spalling and chipping.
In use as a cutting element in tools such as those mentioned above,
the body of PCD material normally wears according to the following
progression: smooth wear, woody wear, accelerated wear, spalling.
Spalling usually occurs when the wear scar reaches the top working
surface, and results in catastrophic wear failure.
As used herein, the term "barrel chipping" refers to chipping in
the body of PCD material below a main wear-scar.
Smooth wear as used herein refers to wear occurring at the diamond
grain level where individual grains or fractions of grains are
removed.
Woody wear as used herein refers to the regime where the wear-scar
becomes irregular at the edges and cracking visible. The rough
appearance of the wear-scar is possibly due to wear processes at a
scale of more than one grain.
As used herein the term spalling refers to catastrophic failure due
to wear cracks propagating to top of the PCD body acting as a
cutter table.
Durability here refers to distance cut before cutter failure.
High-durability cutters tend to maintain cutting integrity but
eventually become ineffective due to formation of a very large
wear-scar and hence impractical load application requirements.
Prevention of spalling would increase lifetime/durability of the
cutter and there is therefore a need for a product in which
spalling is partially or completely inhibited and a method of
producing such a cutter.
SUMMARY
Viewed from a first aspect there is provided a polycrystalline
superhard construction comprising: a body of polycrystalline
superhard material; a substrate of hard material bonded to the body
of polycrystalline superhard material along an interface; wherein
the body of polycrystalline superhard material comprises a first
region and a second region, the first region abutting the substrate
along the interface and the second region being bonded to the first
region along a further interface, the second region defining a rake
face, a chamfer, a cutting edge, and at least a part of a flank
face, the cutting edge being defined by an edge of the flank face
joined to the chamfer, the chamfer extending between the cutting
edge and the rake face; the first region having a first thickness
and the second region having a second thickness; the chamfer having
a height in a plane parallel to the plane through which the
longitudinal axis of the polycrystalline superhard construction
extends, the height of the chamfer being less than the thickness of
the second region; the first region comprising a material having
coarser grains than the material of the second region.
Viewed from a second aspect there is provided a cutter for boring
into the earth comprising the above-mentioned polycrystalline
superhard construction.
Viewed from a third aspect there is provided a PCD element for a
rotary shear bit for boring into the earth, for a percussion drill
bit or for a pick for mining or asphalt degradation, comprising the
above-described polycrystalline superhard construction.
Viewed from a fourth aspect there is provided a drill bit or a
component of a drill bit for boring into the earth, comprising the
above-described polycrystalline superhard construction.
Viewed from a fifth aspect there is provided a method for making a
polycrystalline superhard construction, the method comprising:
providing a first plurality of aggregate masses comprising diamond
grains having a first mean size, at least one second aggregate mass
comprising diamond grains having a second mean size; arranging the
first aggregate mass on the second aggregate mass to form a
pre-sinter assembly together with a body of material for forming a
substrate; the first region comprising a material having coarser
grains than the material of the second region; and treating the
pre-sinter assembly in the presence of a catalyst material for
diamond at an ultra-high pressure and high temperature at which
diamond is more thermodynamically stable than graphite to sinter
together the diamond grains and a substrate bonded thereto along an
interface to form an integral PCD construction comprising a first
region of PCD bonded to a second region of PCD, the first region
being bonded to the substrate; the first region having a first
thickness and the second region having a second thickness; the
second region defining a rake face, a cutting edge, and at least a
part of a flank face; the method further comprising:
forming a chamfer in the flank face, the cutting edge being defined
by an edge of the flank face joined to the chamfer, the chamfer
extending between the cutting edge and the rake face, the chamfer
having a height in a plane parallel to the plane through which the
longitudinal axis of the superhard construction extends, the height
of the chamfer being less than the thickness of the second
region.
BRIEF DESCRIPTION OF THE DRAWINGS
Non-limiting embodiments will now be described by way of example
and with reference to the accompanying drawings, in which:
FIG. 1 is schematic partial cross-section through a first
embodiment of a cutter;
FIG. 2 is a schematic partial cross-section through the cutter of
FIG. 1 showing progression of a wear scar;
FIG. 3 is a schematic partial cross-section through the cutter of
FIG. 1 showing further progression of a wear scar;
FIG. 4a is a side view of a conventional cutter showing the wear
scar for a predetermined number of passes;
FIG. 4b is a side view of an embodiment of a cutter showing the
wear scar for the same predetermined number of passes as that
applied to the cutter of FIG. 4a;
FIG. 5a is a side view of the conventional cutter of FIG. 4a after
a further number of passes at which spalling has occurred;
FIG. 5b is a side view of the embodiment of a cutter shown in FIG.
4b after the same number of passes applied to the conventional
cutter of FIG. 5a;
FIG. 6 is a side view of the embodiment of the cutter of FIG. 4b
after a further number of passes;
FIG. 7a is a side view of a further conventional cutter after a
predetermined number of passes;
FIG. 7b is a side view of a further embodiment of a cutter showing
the wear scar for the same predetermined number of passes as that
applied to the cutter of FIG. 7a;
FIG. 8a is a side view of the conventional cutter of FIG. 7a after
a further number of passes at which spalling has occurred;
FIG. 8b is a side view of the embodiment of a cutter shown in FIG.
7b after the same number of passes applied to the conventional
cutter of FIG. 7a; and
FIG. 9 is a side view of the embodiment of the cutter of FIG. 7b
after a further number of passes.
DETAILED DESCRIPTION OF EMBODIMENTS
As used herein, a "superhard material" is a material having a
Vickers hardness of at least about 25 GPa. Diamond and cubic boron
nitride (cBN) material are examples of superhard materials.
As used herein, a "superhard construction" means a construction
comprising polycrystalline superhard material or superhard
composite material, or comprising polycrystalline superhard
material and superhard composite material.
As used herein "polycrystalline superhard" (PCS) material comprises
a mass of grains of a superhard material and interstices between
the superhard grains, the content of the superhard grains being at
least about 50 percent of the material by volume. The grains may
comprise diamond or cubic boron nitride (cBN).
As used herein, polycrystalline diamond (PCD) is a PCS material
comprising a mass of diamond grains, a substantial portion of which
are directly inter-bonded with each other and in which the content
of diamond is at least about 80 volume percent of the material with
"interstices" or "interstitial regions" between the diamond grains
of PCD material.
As used herein, polycrystalline cubic boron nitride (PCBN) material
is a PCS material comprising a mass of cBN grains dispersed within
a wear resistant matrix, which may comprise ceramic or metal
material, or both, and in which the content of cBN is at least
about 50 volume percent of the material. In some embodiments of
PCBN material, the content of cBN grains is at least about 60
volume percent, at least about 70 volume percent or at least about
80 volume percent. Embodiments of superhard material may comprise
grains of superhard materials dispersed within a hard matrix,
wherein the hard matrix preferably comprises ceramic material as a
major component, the ceramic material preferably being selected
from silicon carbide, titanium nitride and titanium
carbo-nitride.
A cutter 1 according to a first embodiment is shown in FIGS. 1 to
3. The cutter 1 comprises a substrate 2 bonded along an interface 3
to a body of polycrystalline diamond (PCD) material 4. The body of
PCD material comprises a first region 6 of PCD material bonded to
the substrate 2 and a second region 8 of PCD material bonded to the
first region 6 along a further interface 10. The exposed surface 12
of the second region 8 forms a rake face 14, a chamfer 20 extending
between the rake face 14 and a cutting edge 16, and at least a part
of a flank 18 of the cutter 1, the cutting edge 16 being defined by
the edge of the chamfer 20 and the flank 16.
The "rake face" 14 of the cutter 1 is the surface or surfaces over
which the chips of material being cut flow when the cutter 1 is
used to cut material from a body, the rake face 14 directing the
flow of newly formed chips, and is commonly referred to as the top
face of the cutter. As used herein, "chips" are the pieces of a
body removed from the work surface of the body by the cutter 1 in
use.
As used herein, the "flank" 18 of the cutter 1 is the surface or
surfaces of the cutter 1 that passes over the surface produced on
the body of material being cut by the cutter 1 and is commonly
referred to as the side or barrel of the cutter. The flank 18 may
provide a clearance from the body and may comprise more than one
flank face.
As used herein, a "cutting edge" 16 is intended to perform cutting
of a body in use. A "rounded cutting edge" is a cutting edge that
is formed by a rounded transition between the rake face and the
flank.
As used herein, a "wear scar" is a surface of a cutter formed in
use by the removal of a volume of cutter material due to wear of
the cutter. A flank face may comprise a wear scar. As a cutter
wears in use, material may be progressively removed from proximate
the cutting edge, thereby continually redefining the position and
shape of the cutting edge, rake face and flank as the wear scar
forms. As used herein, it is understood that the term "cutting
edge" refers to the actual cutting edge, defined functionally as
above, at any particular stage or at more than one stage of the
cutter wear progression up to failure of the cutter, including but
not limited to the cutter in a substantially unworn or unused
state.
With reference to FIGS. 1 to 3, the chamfer 20 is formed in the
structure adjacent the cutting edge 16 and flank 18. The rake face
14 is therefore joined to the flank 18 by the chamfer 20 which
extends from the cutting edge 16 to the rake face 14, and lies in a
plane at a predetermined angle .theta. to the plane perpendicular
to the plane in which the longitudinal axis of the cutter 1
extends. In some embodiments, this chamfer angle is up to around 45
degrees.
The interface 10 between the first and second regions of PCD
material, 6 and 8, is spaced from the cutting edge 16 which is
defined by the second region 8. Therefore, the thickness of the
second region 8 is greater than the vertical height of the chamfer
20.
The thickness of the first region 6 of PCD material is
substantially greater than the thickness of the second region 8.
For example, in some embodiments, the thickness of the second
region 8 is up to around 600 microns and the thickness of the first
region 6 is around 1200-1800 microns. In some embodiments, the
thickness of the second region 8 exceeds the vertical chamfer
height by around 100-400 microns and the vertical height of the
chamfer 20 may be, for example, around 400 microns.
In FIGS. 1 to 3, the hashed lines 22, 24 represent the work face
making an angle .PHI. with the longitudinal axis of the cutter 1.
This angle .PHI. is also referred to as the back-rake angle.
As the cutter 1 wears, the wear on the cutter 1 is shown by a shift
in the hashed line 22 to the position denoted by the second hashed
line 24. FIG. 1 shows the first stage where all cutting is carried
out by the second region 8 of the body of PCD material. The first
hashed line 22 shows the start of the cut and the second hashed
line 24 shows where the wear has reached the interface 10 between
the first and second regions 6, 8 of PCD material. The initial back
rake angle .PHI. and its progress shift is thereby shown in FIG. 1
as the cutter 1 wears during use, the wear-flat eventually reaching
the thicker/softer PCD layer of the first region 6.
FIG. 2 shows further wear of the cutter 1 after additional use and
it will be seen that the wear flat proceeds more quickly in the
softer layer of the first region 6 of PCD material than in the more
wear resistant layer of the second region 8 of the body of PCD
material. The wear has therefore progressed into the first region 6
and, as the material of the first region 6 wears faster than the
material of the second region 8, the angle of the cutting face
(denoted by the back rake angle .PHI.) gradually decreases so that
the wear of the first region 6 is greater than that of the second
region 8.
This may have the effect of slowing down the progression of the
wear-flat in the chamfer region 20.
FIG. 3 shows a further stage where the wear flat has reached the
rake face 14 as it intersects the chamfer 20 and has also reached
the interface 3 of the first region 6 and the substrate 2. Further
wear and retardation of the wear flat in the chamfer region 20
delays the spalling which may occur when the wear flat reaches the
corner of the chamfer 20 as denoted by the second hashed line
24.
Once the wear reaches the top of the chamfer 20, this could lead to
spalling and, once the wear reaches the interface 3 between the
substrate 2 and the first region 6, the cutter 1 may have reached
the end of its useful working life.
FIG. 4a is a side view of a conventional cutter showing the wear
scar for a predetermined number of passes. It will be seen that the
wear on this cutter is greater than that on the cutter of FIG. 4b
which is in accordance with a first embodiment for the same
predetermined number of passes as that applied to the cutter of
FIG. 4a.
FIG. 5a is a side view of the conventional cutter of FIG. 4a after
a further number of passes at which spalling has occurred. It will
be seen that there is extensive spalling damage to the cutter
whilst the cutter of FIG. 4b after the same number of passes
applied to the conventional cutter shows only a small amount of
wear.
FIG. 6 is a side view of the embodiment of the cutter of FIG. 4b
after a further number of passes with the onset of spalling
behaviour.
FIG. 7a is a side view of a further conventional cutter after a
predetermined number of passes and FIG. 7b is a side view of a
further embodiment of a cutter showing the wear scar for the same
predetermined number of passes as that applied to the cutter of
FIG. 7a. It will be seen that in the embodiment shown in FIG. 7b,
whilst the wear scar is larger than that shown in FIG. 7a, the wear
is all in the woody region.
FIG. 8a is a side view of the conventional cutter of FIG. 7a after
a further number of passes at which spalling has occurred. FIG. 8b
is a side view of the embodiment of a cutter shown in FIG. 7b after
the same number of passes applied to the conventional cutter of
FIG. 8a. In the embodiment of FIG. 8b, the cutter has maintained a
sharp cutting edge although the wear scar is larger than that in
the cutter of FIG. 8a.
FIG. 9 is a side view of the embodiment of the cutter of FIG. 8b
after a further number of passes. The cutter has failed due to the
large wear scar although a sharp cutting edge is still visible.
The material forming the second region 8 is chosen to be
significantly more wear resistant than the material forming the
first region 6. The significantly lower wear resistance of the
first region 6 assists in enabling a desired wear pattern to be
created in use.
The cutter 1 may be fabricated as follows.
As used herein, a "green body" is a body comprising grains to be
sintered and a means of holding the grains together, such as a
binder, for example an organic binder. Embodiments of superhard
constructions may be made by a method including preparing a green
body comprising grains of superhard material and a binder, such as
an organic binder. The green body may also comprise catalyst
material for promoting the sintering of the superhard grains. The
green body may be made by combining the grains with the binder and
forming them into a body having substantially the same general
shape as that of the intended sintered body, and drying the binder.
At least some of the binder material may be removed by, for
example, burning it off. The green body may be formed by a method
including a compaction process, injection or other molding,
extrusion, deposition modelling or other methods. The green body
may be formed from components comprising the grains and a binder,
the components being in the form of sheets, blocks or discs, for
example, and the green body may itself be formed from green bodies.
For example, the green body for the superhard construction may be
formed from distinct green bodies for each of the respective
regions 6, 8, which may be formed separately into generally the
intended shapes of the respective regions and combined to form a
boundary defined by a contact interface.
One embodiment of a method for making a green body includes
providing tape cast sheets, each sheet comprising a plurality of
diamond grains bonded together by a binder, such as a water-based
organic binder, and stacking the sheets on top of one another and
on top of a support body. Different sheets comprising diamond
grains having different size distributions, diamond content or
additives may be selectively stacked to achieve a desired
structure. The sheets may be made by a method known in the art,
such as extrusion or tape casting methods, wherein slurry
comprising diamond grains and a binder material is laid onto a
surface and allowed to dry. Other methods for making
diamond-bearing sheets may also be used, such as described in U.S.
Pat. Nos. 5,766,394 and 6,446,740. Alternative methods for
depositing diamond-bearing layers include spraying methods, such as
thermal spraying.
A green body for the superhard construction may be placed onto a
substrate, such as a cemented carbide substrate to form a
pre-sinter assembly, which may be encapsulated in a capsule for an
ultra-high pressure furnace, as is known in the art. The substrate
may provide a source of catalyst material for promoting the
sintering of the superhard grains. In some embodiments, the
superhard grains may be diamond grains and the substrate may be
cobalt-cemented tungsten carbide, the cobalt in the substrate being
a source of catalyst for sintering the diamond grains. The
pre-sinter assembly may comprise an additional source of catalyst
material.
In one version, the method may include loading the capsule
comprising a pre-sinter assembly into a press and subjecting the
green body to an ultra-high pressure and a temperature at which the
superhard material is thermodynamically stable to sinter the
superhard grains. In one embodiment, the green body may comprise
diamond grains and the pressure is at least about 5 GPa and the
temperature is at least about 1,300 degrees centigrade. In one
embodiment, the green body may comprise cBN grains and the pressure
is at least about 3 GPa and the temperature is at least about 900
degrees centigrade.
An embodiment of a superhard construction may be made by a method
including providing a PCD structure and a diamond composite
structure, forming each structure into the respective complementary
shapes, assembling the PCD structure and the diamond composite
structure onto a cemented carbide substrate to form an unjoined
assembly, and subjecting the unjoined assembly to a pressure of at
least about 5.5 GPa and a temperature of at least about 1,250
degrees centigrade to form a PCD construction.
A version of the method may include making a diamond composite
structure by means of a method disclosed, for example, in PCT
application publication number WO2009/128034 for making a
super-hard enhanced hard-metal material. A powder blend comprising
diamond particles, particles of carbide material and a metal binder
material, such as cobalt may be prepared by combining these
particles and blending them together. Any effective powder
preparation technology may be used to blend the powders, such as
wet or dry multi-directional mixing, planetary ball milling and
high shear mixing with a homogenizer. In one embodiment, the mean
size of the diamond particles may be at least about 50 microns and
they may be combined with other particles simply by stirring the
powders together by hand. In one version of the method, precursor
materials suitable for subsequent conversion into carbide material
or binder material may be included in the powder blend, and in one
version of the method, metal binder material may be introduced in a
form suitable for infiltration into a green body. The powder blend
may be deposited in a die or mold and compacted to form a green
body, for example by uni-axial compaction or other compaction
method, such as cold isostatic pressing (CIP). The green body may
be subjected to a sintering process known in the art for sintering
similar materials without the presence of diamond, such as may be
used to sinter cemented tungsten carbide, to form a sintered
article. For example, the green body may be sintered by means of
hot pressing or spark plasma sintering. The diamond particles may
wholly or partially convert to a non-diamond form of carbon, such
as graphite, depending on the sintering conditions. The sintered
article may be subjected to a subsequent treatment at a pressure
and temperature at which diamond is thermally stable to convert
some or all of the non-diamond carbon back into diamond and produce
a diamond composite structure. An ultra-high pressure furnace well
known in the art of diamond synthesis and the pressure may be at
least about 5.5 GPa and the temperature may be at least about 1,250
degrees centigrade.
An embodiment of a superhard construction may be made by a method
including providing a PCD structure and a precursor structure for a
diamond composite structure, forming each structure into the
respective complementary shapes, assembling the PCD structure and
the diamond composite structure onto a cemented carbide substrate
to form an unjoined assembly, and subjecting the unjoined assembly
to a pressure of at least about 5.5 GPa and a temperature of at
least about 1,250 degrees centigrade to form a PCD construction.
The precursor structure may comprise carbide particles and diamond
or non-diamond carbon material, such as graphite, and a binder
material comprising a metal, such as cobalt. The precursor
structure may be a green body formed by compacting a powder blend
comprising particles of diamond or non-diamond carbon and particles
of carbide material and compacting the powder blend.
The present disclosure may be further illustrated by the following
examples which are not intended to be limiting.
EXAMPLE 1
In one embodiment, ultra-high pressure and temperature may be used
to sinter the superhard construction at approximately 6.8 GPa or
higher. The resulting top layer, namely the second region 8 may
comprise sintered fine grains of multimodal diamond, with average
final grain size of, for example, approximately 0.1 to 10 .mu.m, 1
to 8 .mu.m, 3 to 6 .mu.m or 3.5 to 4.5 .mu.m. This second region 8
may be, for example, between 400 .mu.m and 1000 .mu.m thick, or
between 600 .mu.m and 800 .mu.m thick. The vertical height of the
chamfer 20 may be, for example, between 350.mu.m and 450 .mu.m,
such as around 400 .mu.m. The first region 6 may comprise less wear
resistant sintered coarser grains of multimodal diamond of average
final size of, for example, approximately 6.0 to 20 .mu.m, 8 to 17
.mu.m, 6 to 17 .mu.m or 8.0 to 9.0 .mu.m. This first region 6 may
be, for example between about 1200 .mu.m and 1800 .mu.m thick, such
as between about 1400 .mu.m and 1600 .mu.m thick.
Such an embodiment of a PCD compact may, for example, be prepared
as follows. 2.5 g of a first multimodal diamond powder mix having
an average particle size of approximately 7 .mu.m and 2.5g of a
second multimodal diamond powder mix having an average particle
size of approximately 11 .mu.m and 3 weight percent VC--TiC admix
may be prepared and bound into organic tape which is easily
removable by pre-heating, using methods well known in the art.
Sufficient discs of the first tape to form a top sintered layer of
approximately 600 .mu.m final thickness may be placed in a Niobium
canister, and similarly sufficient discs of the second tape to form
the underlying sintered layer of approximately 1600 .mu.m final
thickness may be placed in the canister on top of the first discs.
A tungsten carbide substrate is then placed in the Niobium canister
on top of the second discs, the canister is sealed and then
heat-treated to remove the organic binders. The canister may be
treated at ultra-high pressure and temperature (for example at
approximately 1600.degree. C. and 6.8 GPa or greater). After
sintering, the PCD cutters may be ground to size including a
45.degree. chamfer of approximately 0.4 mm height on the body of
PCD material so produced. Cutters produced according to the above
have been subjected to wear tests (as shown in FIGS. 4b, 5b and 6)
by suitably preparing them as would be appreciated by the skilled
person, to machine a granite block mounted on a vertical turret
milling apparatus and counting the number of passes before failure.
The average number of passes achieved was approximately 65% better
than that of a commercial benchmark, namely that shown and
described above with reference to FIGS. 4a and 5a.
EXAMPLE 2
In a further embodiment, the second region 8 may comprise coarse
sintered grains of multimodal diamond, with average final size of
approximately 4.5-5.5 .mu.m. In this embodiment, the source diamond
may be admixed with any combination of, for example TiC, TaC, VC,
carbonitrides of Ti, Ta, V, in amounts 1% to 6% by weight. An
example of such an admix is 2-4% TiC--VC. This second region 8 may
be, for example between 400 .mu.m and 1000 .mu.m thick, such as
between 600 .mu.m and 800 .mu.m thick. The chamfer angle is
approximately 45.degree. with vertical height of the chamfer 20
being, for example between around 350 .mu.m and 450 .mu.m, such as
around 400 .mu.m. The first region 6 may comprise less wear
resistant sintered coarser grains of multimodal diamond of average
final size of approximately 8.0-9.0 .mu.m. This first region 6 may,
for example, be between about 1200 .mu.m and 1800 .mu.m thick, such
as between about 1400.mu.m and 1600 .mu.m thick.
Such an embodiment of a PCD compact may, for example, be prepared
as follows. 2.5 g of two multimodal diamond powder mixes having
average particle sizes of approximately 5 .mu.m and approximately
11 .mu.m may be prepared and bound into organic tape easily removed
by pre-heating, using methods well known in the art. Sufficient
discs of the first tape to form a top sintered layer of
approximately 600 .mu.m final thickness are placed in a Niobium
canister, and similarly sufficient discs of the second tape to form
the underlying sintered layer of approximately 1600 .mu.m final
thickness are placed in the canister on top of the first discs. A
tungsten carbide substrate is then placed in the Niobium canister
on top of the second discs, the canister is sealed and then
heat-treated to remove the organic binders. The canister may be
treated at ultra-high pressure and temperature (such as
approximately 1600.degree. C. and 6.8 GPa). After sintering, the
PCD cutters may be ground to size including a 45.degree. chamfer of
0.4 mm height on the body of the PCD material. Cutters produced in
this manner were subjected to wear tests by suitably preparing them
as would be appreciated by the skilled person, to machine a granite
block mounted on a vertical turret milling apparatus and counting
the number of passes before failure. The average number of passes
achieved, as illustrated in FIGS. 7b, 8b and 9, outperformed a
corresponding conventional cutter (as shown in FIGS. 7a and 8a)
which had not been surface-treated by a factor of about three.
Whilst not wishing to be bound by a particular theory, the above
results indicate that more wear-resistant finer-grain PCD material
on less wear-resistant coarser-grain PCD material may significantly
enhance the durability of the cutter produced according to some
embodiments described herein. The wear starts in the thinner, more
wear-resistant layer of the second region 8 and progresses to the
underlying thicker, less wear-resistant layer of the first region 6
which is bonded to the substrate 2. Unlike in typical monolayer
configurations known in the art, these configuration may assist in
diverting the wear scar downwards into the barrel of the PCD body,
instead of the typical behaviour, in which the wear-scar generates
cracks which move to the free surfaces of the cutter and result in
failure through spalling. This has the effect that the wear
behaviour in cutters according to some embodiments may remain
longer in the smooth to "woody" wear region, before eventually
spalling. Performance may be further improved when the interface 3
between the body of PCD material and the substrate 2 is non-planar
(not shown).
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